Automatic telephone system



Julyl 7, 1928,

. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM 2 insets-sheet 1 Filled llMay25, 1927 E'uciul 11E ET'ahlik July 17, 1928.

R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM luv-anion FudE Z Z-L F STEZ-dikill! Patented July 17, 1928.

eairsu sures PATENT cl rics.

RUDbLPH STEE L K or on onso rnnrnors assrqnon 'ro REsE vn 10mm COMPANY,OF KANSAS CITY, MrssoURr, A CORPORATION or DELAWARE.

"AUTOMATIC newt-Hoes SYSTEM.

Application filed May 25,

The present invention relates in general to automatic telephone systems,and is concerned more particularly with such systems in which a linefinder is employed to connect an idle selecting switch with theterminals of a calling line, and the principal object of the invention,briefly stated,is theprovision of a newand improved finder system, whichis thoroughly reliable in its operation, and which can be manufacturedand maintained at a reasonable cost.

. The presentinvention relates more particularly to finder switches ofthe full selective type, that is to such aisystem in which the finderswitch is moved first in one direction in search of the level.containing the calling line, and then in a coordinatedirection in searchof the contacts of that line in the selected level. In one embodiment ofmy invention Iv employ as a finder switch, the well known Strowgerconnector, which is that shownin the Patent 815,176 issued to Keith,Erickson and Erickson, with the circuits and mechanical structurealtered in accordance with the objects of my invention. Thistype ofswitch has been used in such systems heretofore, in which systems thefinder switches proper were controlled by and through a group of commoncontrol equipment. The successful operation .of such a system isdependent largely upon the operation of the common control equipment,and if that control equipment becomes defective or out of order, arelatively large group of finder switches, and consequently larger groupof subscriber lines was thrown out of service temporarily. Accordingly,as f a further object of my invention I provide a new and improvedselective finder system, in which the finder switches are self containedand self controlled, and in which the control equipment common to agroup of finder switches is reduced in quantity and function to renderthe operation of the system more reliable.

In finder switch systems which have been devised heretofore, a largegroup of finder switches are available to pick-up calls from a group ofsubscribers lines, those switches being allotted for service one at atime by 1927. Serial no. 193.960.

means of afinder allotter. The finder a1- lotter so employed constitutesa common con-. trol equipment, and if that equipmentiS faulty a finderswitch group is thrown out of service; In recognization of this fact,systems have been devised heretofore with duplicate or tandem finderallotters, which alternately function to allot a finder switch forservice. Accordingly a further object of this invention is to provide anew and improved finder allotter of the tandem type, and to providesimplified circuitconnections therefor, the improvements tending torender the finder allotterequipment more reliable.

In selective finder systems which have been devised heretofore and ofwhich I: 'am aware, the removal of the receiver from the switchhook ofthe. calling telephone operates the line equipment, to energize thelevel relay, to mark the level of the calling line in the finder switchbank. 'This level marking re,- lay .was used in commonwith all the linesof that particular level. Therefore in a finder switch system havingfinder switches of a 10-level-capacity, ten of, such 'relaysarere' Iquired for each group. The usual plurality of level marking relays runsup the initial cost of the system, and increases thenumber of, contactsprings employed, thereby increasing the likelihood of dirty contactsand con sequent higher maintenance cost. As afurther object ofmyinvention I provide a new and improved level markingarrange'ment, inwhich the number of level marking relays has been reduced to one, andthe number of contact springs further reduced to render the system lessexpensive-and more reliable. I

Further. objects of. my invention, not sp'ecifically mentioned here,will be apparent from the detailedv description and claims which follow.The drawings comprising Figs. 1 and 2, when arranged with Fig. 1 aboveFig. 2 with. correspondingly numbered lines in alignment, showssuflicient details to enable a clear understanding of my invention.

Referring now particularly to Fig. -1, I

show a calling subscribers line A, terminatcut-off relays 1 and 2, whichare operated responsive to acall upon that line to mark its destinationat the finder switch banks and to start the finder switch to connectwith it.

' The finder switchF comprises a Stro'wgeri two-motion switch mechanism,actuated by vertical magnet 12, rotary magnet 13 and release magnet 17and controlled by the tour control relays 3, 1, 5, and 6.v This finderis equipped with a vertical wiper 53 which engages the contacts of 'avertical bank VB as the finder switch shaft (not shown) is steppedupward by the verticalmagnet. The

mechanical features of this vertical wiper and vertical bank are notnew, and do not from an integral part of the present invention. Such awiperv and banks applied to a Strowger connector, is shown on page 69,the 1925 edition of the book Principles of Automatic Telephony by HarryB. Mahoney, and'a description of its operation-is made in the ensuingpages' ot'that text. Finder switch F also carries the customary linewipers 31 and 33rand the p'rivate wiper 32, which are rotated intoengagement with the'contacts of a particular level after that level hasbeen selected by the finder through the agency of the vertical bankr Inthe circuit shown, the finder switch F is ar ranged to operate in avertical direction until the vertical wiper 53- encounters a groundedcontact, thatcontact being grounded by the line equipment of a callingline to level;

mark thelevel containing that line. WVhen the vertical Wiper 53encounters this grounded contact, the control relays of the finder F arealtered so that the vertical magnet is open circuited, and the rotarymagnet impulsed to drive the wipers 31 to 33 into en.- gagement with thecontacts of the selected The rotary action of the finder F, continuesuntil the private -wiper;32 encounters an ungrounded contact, at whichtime the finder switches through .to establish a connection from thecalling line to the selector switch S. The selector switch S, is a wellknown Strowger selector switch, whose wipers aremoved first in'avertical direction under the control of the calling device at thesubscriber s station, and then moved automatically in a horizontaldirection to select the-first idletrunk in the selected level.

Referring now to Fig. 2 I show finder al lotters FA and FA", eachco'mprising'the V double'ended wipers which sweep-over a row ofcontacts, and a motor magnet for driving the wipers; Mechanically thesefinder allotters are like the well known rotary lineswitch, whose wipersmove in a forward di rection .only,hav1ng no normal position andparticular line.

selected finder through the finder allotter FAR Similarly relay 103 isassociated with the finder allotter 1iA .Relay 101 is associated withthe vertical bank circuits, being energized whenever callis initiated inthe group, regardless ot'thele'vel containing that v The" energiza'tionof relay 101 projects agrounded circuit through relays 102 and 103inmultiple, one or the other of'those relays energizing over thatcircuit to start the finder switch which it has preselected. I v p InFig. 2 I also show the supervisory relay104, which is energized inseries with the release magnet of a finder to extend super visorycircuits as willbe pointed out. The banks of finder allotters-FA andFAeach have 25 contacts in a row, over which the re spective wipers aredriven. Thus if it Were desired to do so, each finder allotter could'establishcircuits with 25'-separate finder switches. IIowever, sincethefinderF is of the100 line type, that is, there are 100 contactrsetsavailable to its wipers 21 tor33, it is not necessary that finderallottersFA and FA each have access to 25' finders. Such 'anarrangementwould give the line group containing line A 50 finder switches, which ismore than is necessary. It hasbeen found that trafiic in anautomaticexchange, can

the number of'calls lost because all of the finders available to thelines are busy. In the system shown in the present application, I haveprovided 20 finders, accessible through both of the. finder allotters.In the finder allotter FA, the finder switches are accessible in aregularorder, that is, the wipers 110112 on rotating in the directionofthe arrows, encounters finder. switches Nos.*1 to 20 in consecutiveorder; In finder allotter FA I have reversed the allotment of thefinders, so that the wipers 113 to 1141, upon rotating in the directionof the arrows, encounters finder No.20 first, and then proceeds to theNo. 1 contact last, as will be more clearly brought out hereinafter.Since there are 25 contacts in the switch banks, 21 of. which h'avebeenemployed the remaining four are unusedand made permanently busy byground connection, in the banks over which the wiper-i110 otthe findernew- 14.:

allotter- FA sweeps and the wiper 113 of the finder allotter FA sweeps.'A number of finders accessible to;- the line group contai'ning' line Acan be increased to 24 by. removing the permanent busy connections referred' to above and connecting the added four finders to the respectivebank terminals.

If the traflic in the group require more than 24 finders, ordinaryprinciples of trunk grading can be employed, and the added findersprovided as required. To do this certain portions of thefinders would becommon to both finder al'lotters, and other find.- ers' individual toeach of the finder allotters, a change of this'kind beingpossiblewithout departing from the scope and spirit of this invention. i

Throughout the drawings I have shown a plurality of batteries, to avoidunnecessary complication of the figures. In an installation of thesystem of my invention. there would be but one battery, preferably withits positive pole grounded.

When the subscriber at station A raises his receiver to initiate a call,line relay 2 is operated over the loop including the calling station,and upon operating removes the ground potential from contact 29, therebymarking that line calling-to the finder F, so that switch can establisha connection to it. Since the finder bank number of substation A isassumed to be 85, line relay 2, upon energizing places a ground upon theeight vertical bank contacts over which the vertical wiper 53 sweeps.This ground. completes a circuit for the start relay 101 in. serice withresistance such as 82, to energize that relay to start the finderequipment in motion. It will be noted that normally the contacts of thevertical bank VB are connected to battery potential placed on themthrough their-respective resistances such as 81 and 82, and the startrelay 101 in series. When the line A initiated the call the eighthvertical bank contact is changed to ground potential the remai'ningcontacts of the bank being maintained at battery potential by theresistances. "By this arrangement the verti cal wiper 53 encountersbattery potential upon all of the contacts except that associated withthe level it is desired to select, that potential serving to shortcircuit the e hange-overrelay to prevent that relay from energiz1ng andcausing the finder to cut-in upon the wrong level.

The energization of startrelay 101,v throws ground out over conductor130, thence through the winding of relays 102fand-103 in parallel, thecircuit of relay 102 being completed through thewinding of motor magnet105 of the finder allotterFA and the circuit of relay 103 beingcompleted through the motor magnet 106 of thefinder allotter' FA". Oneor the'other of theserelays will be energized, it being assumed thatrelay 102 is slightlyfaster than relay 103, that relay will energizefirst and upon-becomingenergized opens the circuit of 103 to prevent itsenergizing. ment is provided on relay 102 to make it taster to pull upthan relay 103, since it is im-. possible to build two relaysihavingexactly the same time constants, as would be necessaryil both relays 102and 103 were to become fully energized at the same time. -When relay 102energizes in series with magnet 105, the re sistance of the winding ofrelay 102 prevents the energization of that magnet. Relay 102 closes acircuit for the start relay 4 of the preselector finder E-causing thatrelay to.

energize and start the finders stepping in a vertical direction insearch of a marked level, that-is the level containing the'line A. Inthe finder F, the impulsing relay 5 is energized over circuits completedby the start relay 4. and upon energizing, delivers an impulse ofcurrent to the vertical magnet 12, that magnet operating to advance theshaft containing the Wipers 31 to 33 and53 one vertical step. Vhen the;vertical magnet 12 has completely energized, it opens in- No specialadj'ustterrupter springs 49, thereby interrupting the circuit of relay5, to permit that relay ,to fall back and op'enthe circuit of thevertical magnet. Wiper 53 upon being elevated onestep encounters batterypotential, which is led over the finder circuits, to short circuit thechange-over relay 6, to prevent that relay from. energizing anddiverting the impulses from-"the, vertical to the, rotary magnet; I 7

"When the wiper 53 encounters the level containing: the line A, batterypotential upon. it is changed to ground potential,- and relay 6- isenergized, in series with relay 5, .the energizing circuitof the formerserving to hold the latter relay ingits energized position. Relay 6opens the circuit of vertical magnet and changesthe impulsing circuit tothe rotary magnet, which =is, immediately energized to advance 1 thewipers one step into the selective level. This arrangement permits thechange-over from vertical to rotary motion of the finder with aminimumloss of time, the action is positive, dependent upon the energizationrather than upon the ideenergizationbf the change-overrelay, as

.has been the custom heretofore. The r0- tary magnet energizes,advancing the switch wlpers, wiper 32 encountering ground potential aslong as it. is standing upon the contacts of, an uncalling or a busyline. Wiper 32 encounters ground, switching relay 3 is short circuited,to prevent its premature operation. When .the contacts of the callingline are encountered, wiper 32 moves-its ground potential, and relay 3energizes to switch the finder through to seize the calling line. Thecalling subscriber then hears dial tone which is conducted to histelephone over iso line conductors and 65, that tone being applied tothe lowerwinding of the line relay 7 of the selector S. The subscriberupon hearing this dial tone operates his calling device in the wellknown manner, to operate the selector Sin accordance with the firstdigit of the number of the wanted telehone. The operation of selector Sis famillar to those skilled in the art, and since it does-not form anintegral part of this invention will not be enumerated in detail at thistime.

Having thus described my invention in general I will now proceed with a.detailed description of its operation.

Line-A calls. I When the subscriber at substation A removes his receiverto initiate a call, line relay 2 is energized over a circuit traceablefrom ground through springs 25, line conductor 20, through the callingdevice, transmitter, receiver and switch-hookof the substation A,negative line conductor 21, springs 23, through the upper winding ofrelay 2 to battery. Upon energ1z1ng, rclay 2, at springs 26 and 27removesground potential from the private contact 29 in the finder bank,thereby rendering the line A in a calling condition and accessible tothe finder switch F. SpringBO at its make contact closes a circuit fromgq'ound through springs 24, conductor 54, resistance 82, conductor' 83,through the winding of start relay 101 to battery, energizing that relaypreparator to starting the finder switch in motion. round upon theconductor 54, places ground potential on the eighth contact in thevertical bank VB, thereby marking that'level to subsequently causethe-finder F to stop opposite'it and to rotate into it in search of thecontact group 28 -30." The operation of springs 26, in addition toremoving ground potential from the bank of contact 29, extends therelease trunk conductor 22 to the normal release conductor 22, therebypreparing circuits over which the line A is subsequently marked busy inthe banks of the connector switch.

,Startz'hg the finder The energization of start relay 101, closes acircuit from ground through springs 128, conductor [130, through thewinding of relav'102,'conductor 136, springs 123, conductor 131,"through springs 126, through the V winding of motor-magnet 105 tobattery,

with a parallel circuit from conductor 130, through relay 103, conductor134,-' springs I18, conduct-M135, through springs137, through thewinding of magnet 106to battery. -Relays 102 and 103 will both start toenergize over the circuit. It is assumed that relay 102 is slightlyfaster to pull up than relay '103,'that relay energizing first,operinafter explaine'chand at springs 117 and 18 opens points in thecontrol circuit for finder allotter FA', to prevent that finder allotterfrom operating atthis time. At springs 119, relay 102 prepares a furtherpoint in the finder allotter kick ofl' circuit, and at springs 1.20,closes a circuit, from ground through these springs, conductor 137,through wiper 112, now assumed to be in engagement with its 20thbank'contact, conductor 71, through the winding of start relay 4, oft-hefinder F, to battery. -Relay 4 energizes over this circuit to startthe finder. v

Vertical impulsz'ng.

' The energization of relay 4, closes a cir cuit for pulsing relay 5,traceable from ground through spring 40 and its make'contact, verticalinterrupter springs 49, .conductor 67, spring 48 and its break contact,springs 41, conductor 68, through rotary interrupter springs 50, throughthe Winding of Relay 5 energizes over this circuit and at springs42closes a clrcult relay 5 to battery.

mittingtha't magnet to fall back and'close springs 49, again establishthe circuit for the pulsing relay 5. The first operation of the verticalmagnet 12 elevates the vertical wiper 53 into engagement with the lowermost contact of the bank VB; The energization of relay 4, at springs 41prepares a point of circuit of switch-over relay 6, that circuit beingtraceable from battery through relay 5, throughrotary interruptersprings 50.

conductor 68, through springs 41, springs-48 and: its break contact,over conductor'67 to the upper terminal of relay 6.. When wiper 53engages the first contact'of the bank VB, battery potential is appliedto the lower terminal of switch-over relay 6 over .circuits conductor83, resistance 81, first contact and wiper 53, conductor 63, spring 36and its traceable frombattery through relay 101,

I through resistance 82 and relay 101. How

ever relay 6 was not operate over this circuit because ofthe relativelyhigh resistance of 82 and relay 101. The operation ofrelay and thevertical magnet 12 continues, along as wiper 3 encounters batterypotentiahin this case for seven steps. 7

Last "vertical impulse.

\Vhen the vertical magnet andfrelay have completed seven cycles ofoperation as above described, they again energize for. the

, eighth time, the magnet 12 advancingthe wiper 53 into engagement withthe'eighth bank contact ofthe bank VB to which conductor 54 isconnected. Since the calling line A terminates in this eighthlevel, andhas placed ground on conductor 54, wiper 53:encountersground. potentialinstead of battery "potential. ,As soon asthe vertical magnet 4 hascompletely. energizedzand opens springs 49, relay 6 energizes over acircuit traceable from ground, spring '27 and its make contact, springs24, conductor 54, eighth bank contact and vertical wiper 5.3, conductor.63, spring 36 and'its break contact, conductor 64, springs 47 lowerwinding of relay 6, conductor 67, spring 48and its break contact,springs 41, conductor 68, rotary interrupter springs 50, through thewindingv of relay 5 to battery.- Relay 6 is energized over this circuitand relay 5 being in an energized position at the moment the circuit wascompleted, remains in an energized position. Relay 6 upon energizinglocks itself through spring 46 audits upper winding to ground at springand its make contact,th ereby maintaining itselfenergized independent ofthe circuit .just traced through its lower winding. v

. Rotary impulsiag.

relay 6 opens the circuit of vertical mag.- net 12, permittingthatmagnet to fallback, Spring makes contact with its make contact, a;circuit is closed for rotary magnet 13,

causing ,that magnet to. become energized immediately since relay 5 isheld energized,

as explained,- above and contacts 42 are therefore closed. Theenergization of rotary magnet 13 advances wiper-s31 and 33 one rotarystep into the selected level, and operateszspring 5t) at the end of thestep to open the circuit of interrupter relay ,5, that relay fallingback to terminate the pulse thereby, permittingthe rotary magnet 13 todeenergizeand at springs reclose the circuit of: relay 5. Sincethecalling line is assumed to have the finder bankdesignation of 85,contact set 28 to 30, inclusive, is the fifth set in the eighth level,therefore the first four contacts of the level willbe grounded, since itisalsoassumed that the other lines in that level are not calling at themoment. A circuit may now be traced from ground through springs 26 and27in multiple, re-

lease trunk conductors 22'andcontact 29 of the first line in the level,wiper 32, conductor 6 3, spring 36 and its break contact con ductor 64,spring 48 and its make Contact, spring 41,. conductor 68, rotaryinterrupter spring 50, through the winding of relay 5 to battery. Relay5 energizes over this; circuit,

at springs 42, closes a circuit through spring 45 andits make contact,through the winding. of the rotary magnet 13 to battery, energizing thatmagnet which advances the wipers 31 to 33 another step and at springs50opens the. circuit of impulsing relay 5. Thisaction continuesforfour-steps, that is as long as wiper 32 encounters grounded contacts.When switch-over relay 6 is energlzed, it closes springs 44,places-ground upon release trunk conductor 61, that ground potentialupon the upper terminal of switchthrough relay 3. As long as wiper 32encounters ground; potential, switch-through relay 3 is short circuited,since ground from the wiper 32 through conductor 63, and is placed onthe lower terminal over a circuit, springs 36 and its break contact.When the rotary magnet has energized for the fifth time, and advancedthewipers 31-to 33, in'- elusive, into engagement with contacts 28 to 30,inclusive, of calling line A, wiper 32 loses ground,-relay 3 being nolonger short circuited energizes over a'circuit traceable from groundedrelease trunk conductor 61, through the winding of relay 3, conductor64, spring48 and its make contact, springs 41, rotary. interrupterspring 50, through the winding of relay 5 to battery. Relay 3 is of highresistance, and relay 5 is of low resistance, relay'3 theretoreenergizes over this c1rcu1t but relay 5 is prevented from energizmg bythe lllglll'GSlStlIlCG of relay 3. Relay 3 upon energizlng closesspr1ngs'34 to Hit) 39, to switch through the ne ative and positive lineconductors of the nder to trunks V 60 and 65, respectivel so thattheselector switch S is seized in t e usual manner; Re-

lay 3 opens at springs 35 a point in the release-circuit of the finderF, and at springs Finder allotter seeks another fiadr. 2

At springs 38, relay 3, closes a circuit from und through those springs,conductor 72,

t rough the 20th bank contactand wiper 111 of the finder allotter FAconductor 138, springs 119, conductor 136, springs 123, springs122,conductor 132, spring 116 and its make contact, through the windingof motor magnet 105 to the'finder allotter FA to battery, with aparallel path from spring 123 through conductor 131, interrupter springs126, through the winding of the magnet 105 to battery. Magnet 105energizes, prepares to advance the wipers 110 to 112, inclusive, onestep. When the finder F switched through to the line A, the circuit ofrelay 101 was opened, permitting that relay to deenergize and at sprin128 removethe ground from the start con uctor 130. The

. removal of ground from the start conductor 130 permits relay 102 tofall back, and at springs 116 and 119 opens the circuit just traced forallotter motor magnet 112, permitting that magnet to fall back andadvance the wipers 110 and 112, inclusive, one step. Sincecontacts 21 to24 of the bank overwhich wiper 110 rotates are grounded,

. motor magnet 105 is again energized over the circuit traceable fromthat ground through wiper 110, spring 116 and its break contact,conductor 132, springs 122, conductor 131, interrupter springs. 126,through the winding of magnet 105 to battery. Magnet 105 energizes,preparing to advance the wipers. anot 1er step, and opening springs 126,to permit itself to fall back. Magnet 105 therefore operates in a buzzerlike fashion, advancing the wipers step-by-step until wiper 110 fails topick-up ground potential.

All finders busy.

Assuming now that the finder F was the last idle finder of the group.When the finder is elevated off-normal by the vertical ated, removingground from the busy common conductor 70, and placing ground upon theconductor 69 to guard the finder and prevent its hein picked up by oneof the finder allotters. I the finder F was the last idle finder,conductor 70 no longer has ground potential on it, since all the'ofi-normal springs of the group are operated. Therefore when Wiper 110of the finder allotter FA encounters the 25th bank contact, it fails topick-up ground. Consequently the finder allotter FA comes to rest oncontact sets 25, of its bank, remaining there until a finder becomesidle, at which time wiper 110 .will again pick up ground from conductor70, and the finder allotterwill move on in search of that'idle finder.

Since finder F was assumed to be'the last idle finder of the group,finder allotter FA would also bestanding on it, since the test wiper 113of that finder would pick up ground potential on all other contacts ofits banks. When the-oif-normal springs 52'are operated, conductor 69 isplaced on ground potential, wiper 113, which is then standing on itssixth bank contact, would pick up that ground, closing a circuit fromthat ground through that wiper, springs 121, through conductor 133, tothe break contact of spring 117 of the relay 112. When the relay'3of thefinder F switches through and opens the circuit of relay 2, as explainedabove, permitting that relay to fall back, the circuit from conductor133 is completed through springs 117, conductor 135, interrupter springs127, magnet 106 to battery. This magnet energizes, interrupting its owncircuit at springs 127, and acts in a buzzer like fashion to advance thewipers of finder allotter FA. Since all'of the other finders of thegroup are busy, the wiper 113 will encounter ground on all the contactsbetween six and twenty-five, inclusive, when it moves Sir;

into connection with its bank contact 1, to

which conductor 70 is connected, it will lose its ground potential andthe wiper-s will come to rest on that contact. Thus it will be seen thatboth of the finder allotters are alined upon the resting contact,pending the unbusying of one of the finders of the roup. If somesubscriber in the group shofid attempt to call, he will energize therelay 101 as before, throwing the ground upon the start conductor 130,that ground serving to energize relay 102 or relay 103 as before.

ductor 137, that ground going through wiper 112 now resting on itstwenty-fifth bank contact, over conductor 141 to an overflow meter,registering the call as lost because all the finders of the group werebusy at the time it was made. When one of the finders become idle,assume that the finder F is that magnet 12, ofl'-normal springs 52 areoperfinder, both finder allotters FA and FA As soon as relay 102 pullsup, it will at springs 120 place the ground on conwill position-theirwipers upon it, finder FA rotating from contacts 1 to- 6 and finder FAfrom contacts through 1 to 20.

Simultaneous calls.

. winding of relay 103, conductor 134, springs 11 8, conductor 135,through interrupter springs 127, through the winding of magnet 106 tobattery. The energization of relay 103, opens the circuit over whichfinder allotter FA seeks another idle finder, this circuit having beentraced hereinbefore. Re lay 103 closes at springs 125 a finder startcircuit for the start relay 4 of the finder which it has preselected,energizing that relay to start its operation of the finder in the mannerabove described. WVh'en the finder has switched through, relay 103 isshort.- circuited, having ground from conductor 130 upon its lowerterminals and ground from wiper 114 through springs 124 to its upperterminal. Relay 108 therefore falls back, and since relay 102 is alreadyback both finder allotters FA? and FA start looking for an idle finder.If another call is pending, relays 102 and 103 will be prevented fromenergizing by the actuation of the interrupter springs 126 and 127,respectively, by the operation of the magnets of the finderallotters insearching for an idle finder. -As soon as one or the other of the'allotters findsan' idle finder, the relaycorrespon'ding thereto willenergize, stopping both of the finder allotters in the mannerhereinbefore described. Thus it will be seen that in the case of twosimultaneous calls, the one is handled by a finder controlled throughthe finder allotter FA? and the other by finder controlled through theallotter FA", and if another call is pendingat. the time it iscontrolled through the finder allotter which finds an 'idle'finderfirst.

The above embodiment of my invention has been shown and described by Wayof example only and I am not to be limited by the specific disclosureshown, as there are many modifications and adaptations appar ent to oneskilled in the art, which can be madewithout departing from the scope ofmy invention. V

.Having thus described my invention, what I consider new and desire tohave protected by Letters Patent is pointed out in the appended claims:1

What isclaimed is:

1. In an automatic switch mechanism, two

driving magnets e'achcontrollingan'interrupter-spring, an interrupterrelay commonto said magnets, a circuit for said relay including saidinterrupter springs in series, wipers on said switch, contactsaccessibleto said wipers, means for energizingsaid relay over said circuit tooperate the first of said magnets'under the control of a certain one ofsaid wipers and interrupter springs, means operatedthrough said certainwiper to shunt said certain interrupter spring and to render marycontact to mark saidline calling, wip

ers on said finder having access tos'aid contacts, and means in saidfinder controlled through said wipers to select said marked contacts andto line. 4

3. In an automatic telephone systenl, a subscribers line, afi'nderhaving access thereto,-a primary test contact associated withsaid line and normally maintained at establish a connection to saidbattery potential, at secondary test contact. 2

associated with said line and normally maintained at ground potential,means responsive to the initiation of a call on said line to removeground from said secondary contact and to apply ground potential to saidprimary contact to mark said line calling,

wipers on said finder having access to said contacts, means in saidfinder controlled through said wipers to select said marked contacts andto establish a connection to said line, and means responsive to theestablishment of said connection to remove said.

for removing the potential from one of said contacts and applying thatpotential to the other to mark the line calling, and means in saidfinder including wipers engaging said contacts for moving said finder toselect said each level through a resistance individualto that contact,acalling line, means associated therewithfor marking the contactassociated with the level containing that line and for energizing saidrelay through said resistance, finder switch started through theenergization of said relay, and means in said switch for stopping itwhen said marked contact is engaged.

6. In a telephone system, a finder switch, a group of subscribers linesarranged in sub groups, a testing contact individual to each sub-group,a start relay commonto said group and connected to each of saidcontacts,

' means responsive to "a call on one of said lines to energize saidrelay and to mark only the: contact of the sub-groups containing theline, an'd means controlled by said .relay to start said finder to findsaid calling line.

7.,In a telephone system, a group of lines divided into a plurality ofsubgroups, a finder switch having a wiper, a group of contactsaccessible to said wiper containing a contact for each of saidsubgroups, a relay common to said contact group and connected to thecontacts thereinthrough resistances individual to each contact, meansresponsive to the initiation of a call on one of said lines to energizesaid relay through the resistance of the contact associated with thesubgroup containing the line and to mark that contact selectable by saidwiper, and means controlled by said relay to operate said finder toselect said contact and to connect with said calling line. i

8. In an automatic switch, a pair of test wipers permanently connectedtogether, contacts accessible to said wipers, relays in said switchcontrolled through said wipers and contacts over circuits, includingmeans for rendering the first of said relays responsive to groundpotential and for rendering the second of said relays responsive to zeropotential on said wiper, and means operated by said relays to controlthe operation of said switch.

9. In a telephone system, a finder switch having wipers operable inprimary and secondary motions, a primary test wiper and contacts engagedthereby to control the primary motion of said finder, said contactsnormally carrying a potential placed thereon by battery through a highresistance, lines accessible to said finder, means responsive to theinitiation of a call on one of said lines to mark one of said primarytest contacts and to start said finder in its primary motion,.achange-over relay iI1"S2Lld finder operated when sa d primary test w perengages :said marked contact, and means controlled by said relay to stopthe primary and start the secondary motion of said finder switch.

- 10. In a telephone system, a finder switch having primary andsecondary stepping magnets, interrupter springs controlled by each ofsaid magnets, an interrupter relay, a change-over relay, means forenergizing said interrupter relay to start the operation of said finder,over: a circuit through said interrupter springs in series andrcontactson said change-over relay, means including a primary test wiper and saidchange-over relay removing said interrupter relay from the control ofsaid primary magnet interrupter springs and for subsequently placing itunder the control ofsaid secondarymagnet interrupter springs to operatesaid finder in primary and secondary direction into a desired position.y

11.111 a telephone system, a group of finder. switches, a pair ofdistributor switches having banks of contacts and wipers which engagesaid contacts,connections from individual ones of said finder switchesto the contacts oi the first of said distributor switches in consecutiveorder and extending to the contacts of the second of said distributorswitches in reverse order, means for associating said distributors withidle ones of said finder switches, a line and means responsive to a callthereon to operate one or the other of said-distributors to start itsassociated finder to establish a connection with said line,

12. In, an automatic telephone system, a group of finder switches, twodistributor switches having access to said finders, banks of contacts onsaid distributors, the bank contacts of one distributor being connectedto the finder-sin vconsecutive. order and the bank contacts of the otherconnected in reverse order, means for seizingand operating idle ones ofsaid finder switches through said distributors, means responsive to'theoperation of the last idle finder of the group to stop said distributorson an over fiow contact, and means operated when one of said findersbecomes idle to start said distributors from said over-flow contactsinsearch of said finder.

13. In an automatic telephone systenna group of subscribers lines, agroup of finder switches having access to said lines, two distributorswitches including means for allotting said finders for use one at atime, a start relay associated with each distributor switch, meansresponsive to the initiation'of a call on one ofsaid lines to establisha start circuit to said distributors, said circuit ex tending throughboth of said relays in paral- 101 to energize one of them, and meanscontrolled by said energized relay to open the circuit through the otherrelay and to start said allotted finder to connect with said calling'line. I r v 14. In an automatic switch, a pair ot test Wiperspermanently connected together, a set of contacts accessible to each ofsaid wipers, relays in said switch, circuits for said relays over whichthe first is caused to respond to and the second prevented fromresponding to a given potential on said 10 In witness whereof, Ihereunto subscribe 15 my name this third day of May, A, D. 1927.

RUDOLPH F. sTEHLIK;

